1. Field of the Invention
The present invention relates to an electrically-operated scroll compressor and, also, to a method of assembling the same.
2. Description of Related Art
FIGS. 6 and 7 depict a conventional scroll compressor. As shown therein, a closed container 1 made up of a cylindrical section 1a and a lid section 1b accommodates an electric motor 2 and a scroll assembly 3 disposed above the electric motor 2. The electric motor 2 comprises a stator 2a and a rotor 2b to drive the scroll assembly 3. The scroll assembly 3 comprises a stationary scroll 3a having a wrap element 3a' integrally formed therewith and an orbiting scroll 3b having an orbiting wrap element 3b' integrally formed therewith so as to engage with the stationary wrap element 3a'. A plurality of compression spaces are delimited by the stationary wrap element 3a' and the orbiting wrap element 3b'. The closed container 1 also accommodates a crank shaft 4 for driving the orbiting scroll 3b, a main bearing 5 for supporting a main shaft 4' formed on one end of the crank shaft 4, and an auxiliary bearing 6 disposed on the side opposite to the main bearing 5 to support the other end of the crank shaft 4. The main bearing 5 and the auxiliary bearing 6 are rigidly secured to the internal surface of the closed container 1.
The orbiting wrap element 3b' and the stationary wrap element 3a' are maintained in fixed angular relationship to each other by the use of an Oldham ring 7. The Oldham ring 7 restrains the orbiting scroll 3b from angular displacement while permitting it to undergo circular translation with a variable circular orbiting radius.
The closed container 1 further accommodates a discharge muffler 8 disposed above the scroll assembly 3 and has a discharge chamber 12 defined between the discharge muffler 8 and the stationary scroll 3a. A discharge pipe 10 communicating with the discharge chamber 12 extends through the cylindrical section 1a of the closed container 1 to discharge compressed gas to the outside of the closed container 1. The closed container 1 also has a suction pipe 9 for sucking gas to be compressed from outside, and a check valve 11 mounted on the stationary scroll 3a to prevent reversing motion of the scroll assembly 3.
The scroll compressor of the above-described construction operates as follows.
Low-pressure gas returns through the suction pipe 9 and is introduced to the scroll assembly 3. The gas is then compressed to high-pressure gas by the scroll assembly 3 in which the orbiting scroll 3b undergoes circular translation with respect to the stationary scroll 3a. Thereafter, the high-pressure gas is discharged outside the closed container 1 from the discharge pipe 10, and again low-pressure gas is returned through the suction pipe 9 and circulated to form a well-known compression cycle.
A method of assembling the scroll compressor of FIG. 6 is discussed hereinafter with reference to FIG. 7.
The stator 2a and the rotor 2b of the electric motor 2 are secured to the cylindrical section 1a of the closed container 1 and to the crank shaft 4, respectively, by means of shrinkage fit. The scroll assembly 3 and the main bearing 5 are secured to each other by means of bolts, and the crank shaft 4 is appropriately mounted on the main bearing 5.
As shown in FIG. 7, after the scroll assembly 3, the main bearing 5, and the crank shaft 4 have been assembled, this assembly is inserted into the cylindrical section 1a, and the main bearing 5 is welded to the cylindrical section 1a on the basis of the inside diameter of the cylindrical section 1a. Then, the auxiliary bearing 6 is inserted into and welded to the cylindrical section 1a on the basis of the inside diameter of the cylindrical section 1a.
Because the conventional compressor shown in FIG. 7 uses the inside diameter of the cylindrical section 1a as a reference, which has limitations in accuracy, it is difficult to concentrically align the main bearing 5 with the auxiliary bearing 6.
FIG. 8 depicts another assembling method as disclosed in Japanese Laid-open Patent Publication (unexamined) No. 4-143475. According to this disclosure, the cylindrical section 1a of the closed container 1 has two stepped portions 1e formed on the internal surface thereof for receiving the main bearing 5 and the auxiliary bearing 6, respectively.
The stator 2a and the rotor 2b of the electric motor 2 are first secured to the cylindrical section 1a and to the crank shaft 4, respectively, by means of shrinkage fit. The main bearing 5 and the auxiliary bearing 6 are then inserted into the cylindrical section 1a until they are brought into contact with associated stepped portions 1e of the cylindrical section 1a. Thereafter, the two bearings 5 and 6 are welded to the cylindrical section 1a while they are being concentrically aligned with each other, and the scroll assembly 3 is secured to the main bearing 5.
In the conventional compressor shown in FIG. 8, because the scroll assembly 3 and the main bearing 5 are assembled after undergoing the welding process, foreign substances are likely to enter the scroll assembly 3. As a result, there arises a problem in that high-accuracy assemblage is difficult.